ISG15 and infection: We found a significant increase in levels of IFN-α and IFN-β, interferon-stimulated genes (ISGs) CXCL-10 and ISG15, and the proinflammatory cytokines interleukin-6 (IL-6) and tumor necrosis factor (TNF) at 16 to 24 hpi following infection with N1040A (Fig. 5).